This invention relates to method of making a wide mouth, non-delaminating, multilayer, plastic container and the product of the method. This may be accomplished by making a multilayer preform, blowing it into a bottle, trimming off a portion of the top and curling the trimmed end. In this case, multilayer is defined as a container made from a preform that is either co-injected, sequentially molded, overmolded or other methods known in the industry. An alternative form of the invention involves the nesting of at least two plastic containers defining an open mouth and curling the material adjacent the open mouth to prevent separation of the containers at the mouth.
As used herein xe2x80x9ccurlxe2x80x9d shall be construed to include shapes other than a circular or part circular shapes, for example, oval shapes, folded shapes, flattened rolls or combinations of these.
Suitable materials are those that can be bi-axially oriented for packaging bottles i.e. orientable polymers, preferably heat settable such as, but not limited to, polyesters such as polyethylene terephthalate (PET), polypropylene (PP) and acrylonitrile (AN). As an example PET is used in this description. In the PET container industry, no adhesives are used to keep the different materials adhered to one another. Simple but weak molecular attraction is used to bond layers together.
Generally, plastic containers exhibit enough barrier properties (the means to inhibit the flow of gas or moisture molecules; e.g., oxygen, carbon dioxide, nitrogen, water through the walls of the container) thus protecting or preserving the product within the container so to meet specifications such as shelf life (how long the product will last before spoiling). In many cases, however, the provision of one or more a barrier layers in the container wall is necessary to guarantee adequate shelf life.
The provision of barrier layers is known in the prior art. One method used is to blow mold a container directly from a preform having one or more barrier layers between inner and outer walls. However, the barrier layers do not extend through the neck finish of the container and does not provide 100% barrier coverage in the container. This applies to both containers having a convention threaded finish as well as to wide mouth containers blown directly from wide mouth preforms. This is also true of prior art containers made by a blow and trim method in which the barrier layer(s) stop short of the trim line of the intermediate article blown from a preform. The lack of a substantially 100% barrier coverage limits the ability of the container to prevent product spoilage.
Making a wide mouth PET container by blow and trim or blow trim curl is known in the PET industry. Normally, in the prior art, the barrier coverage does not extend throughout the blown and trimmed container and the barrier layer normally stops short of the upper finish. It is also known that when a multiple layer PET bottle, including a barrier layer or layers in the wall thereof, is mechanically trimmed through the multiple layers, the layers begin to separate due to the weak bonds between layers. Once the layers start to separate, small applied forces continue the layer separation of the stiff walls into the finish and body area of the container and mechanical and visual defects result. The continued separation may resultfrom simply conveying, filling, capping, labeling, shipping the container or the like. A container being trimmed through the barrier layer(s) is preferred as this provides a container with substantially 100% coverage of the protective barrier throughout the container.
However, a container having substantially 100% barrier layer coverage involves the barrier layer(s) being open to the environment. Some barrier materials do not respond well to the exposure to certain agents such as moisture (e.g. water, steam). These barrier materials will perform poorly in that type of environment as the outside agents will follow the barrier layers downwardly throughout the entire container. This is especially true in filling of products where residual products may fall upon the top sealing surface. The net result is a container that does not meet the targeted specifications.
A last area that is a concern is that some barrier materials will prevent a good seal from being formed when using a film material to seal the container. This induction or heat seal is used frequently to provide additional barrier properties across the closure and/or provide tamper evidence (to show that the container was never previously opened). The film material is typically sealed across the top sealing portion of the container. The barrier material can inhibit a proper seal.
Trimming is well known in the plastic industry. There are many varieties of trimmers used to trim plastic containers. There are two general types of trimmers for highly oriented PET containers: the laser trim and the mechanical trim. The laser trimmer has an advantage in that it burns its way through the side walls of a PET container and cauterizes the edges of a multilayer PET container thus holding the multiple layers together. A weakness of this cauterized edge is that it is very narrow and the area immediately under the cut edge can begin separation if exposed to mechanical forces. The laser trimmer also has several disadvantages to it. A slow speed is needed to give precision cuts, smoke is emitted and an edge of material is built up.
Mechanical trimmers, however, cause separation of the multiple layers as the knife used exerts a force against the side wall of the container. As the knife penetrates each layer, the knife exerts a force on the next layer and separation of the layers occurs. Defects that the mechanical trimmer causes can be eliminated by the curling or shaping the edge of the container opening in accordance with the present invention. It has previously been revealed that curling a lip has significant advantages over a blow and trim edge (see Beck U.S. Pat. No. 6,062,408).
In a further example, the barrier termination is uneven and the trim line passes through portions of the barrier layer(s) and the monolayer of polymer.
It is an object of the present invention to provide a method of preventing delamination or separation of multiple layers of a plastic container, with or without, barrier layers at an opening thereof, at which the multiple layers are exposed. The invention provided herein provides a method and a product that eliminates the problems of layer separation by the use of a curled or shaped container lip.
According to the invention there is provided a method of preventing delamination of multiple layers of at least one polymer container having an opening defined by the multiple layers comprising the steps of:
a) providing said container having a opening defined by a perimeter at which the multiple layers are at least partially exposed;
b) heating said perimeter until workable:
c) providing a curling device; and
d) using said device to curl said perimeter sufficiently to inhibit delamination of the layers. The multiple layers may, in a preferred form, be totally exposed.
The angle of curl is preferably at least about 180xc2x0 and more preferably is at least about 270xc2x0 or 360xc2x0.
In a preferred form of the method, the multiple layers comprise at least inner and outer walls separated by at least one barrier layer extending throughout the container. In a further preferred form of the method, the container has been trimmed, from an intermediate blow molded article, through the at least one barrier layer to form the opening and in a more preferred form of the invention the opening has a trimmed edge forming the perimeter and said device curls the perimeter to an extent that the trimmed edge is not exposed to the environment.
In a yet further form of the method, the container comprises separate nested containers.
The invention also includes a container when made by the methods of the present invention.